Outlet or switch box.



M. ROBINSON.

OUTLET .0R SWITCH BO X. APPLIOATION FILED JULY 22. 1911.

1,121,291 Patented De@.15,1914.

M. ROBINSON.

OUTLET OR SWITCH BOX.

APPLICATION ULEB JULY z2, 1911.

1,121,291. Patented Dec. 15, y1914.

2 SHEETS-SHEET 2.

UNTTED sTATEs PATENT OFFICE..-

I EINER. RBINSON, OF NEWTON, MASSACHUSETTS.

' y OUTLET 0R SWITCH Box.

To all whom it'may concern 'Be it known that I, MIN-Fin ROBINSON, a citizen of the United States', residing at lf'Newton, county of VMiddlesex, State of Massachusetts, have invented an Improvement in Outlet or Switch Boxes, ofwhich the following description', in connection wwith the accompanying drawing, is a specifi- `cation, like characters on the drawing representing like parts.

` This invention relates to switch, outlet, or

j u'nctionA boxes for electrical wiring l purposes These boxes are commonly made "llwith a so-called knock-out or sealed portion, that is, with an aperture or partially-formed aperture through the wall of the box which islclosed by a seal or knock-outportion so 1co'lnnectedwith or sustained by the box that `."it.l can be knocked out by a blo'w thereby to 'leave an aperture for the insertion. of a con- `duit. Some boxes are made of steel While others are made of cast iron.,l

"It has heretofore been proposed to make" 'th'eknock-out -portion in a cast-lron box by casting said box with a recess on .both the inside land outside of the wall thereof thereby to leave a thin at web which can be broken Il' entirely satisfactory, however,V4 partly because they are very apt' to break along a ragged line, thus leaving the con-.

duit-receiving aperture with a jagged edge, and partly because if they are made very thin they will n ot cast well, while if they are made thick enough -to cast well they cannot be broken out except by a 'comparatively heavy blowwhich is liable to crack the walls of the box. Moreover, the .present rules concerning outlet -boxes require 40 that the seal or knock-out portion shall have a thickness as nearly equivalent -to that of the walls of the box as possible, and this Y .rule prevents the use of a cast iron box hav-v t ing knock-out portions which are made thin fi as above described. It hasalso been proposed to make the knock-out portion of av cast-iron box with a thin connecting web joining the same to the adjacent walls of the box, but with this construction the knock-out portion can be broken from-the box only by delivering upon it a blow of considerable strength which is liable to crack or otherwise injure the box.

-My present invention has for its general Speccation` of Letters Patent.

Eibya blow. Such knock-outs .have not been Patented Dec. 15, 1914.

Application fried my 22, 1911. semi No. 649,027.

object to providea knocklout portion for a cast metal switch, outlet` or junction box, which is free' from the disadvantages inherent in the knock-out portions of prior cast inetal boxes, and whichcan be readily broken'outby a light blow and yet comply 60 with all the necessary requirements relating to knock-out portions. v More specifically the objects of my invention are to provide a novel knockfoutportion in a cast meta-l box which can be readily broken out with a blow of a'hammer or other implement without danger of Ecracking or breaking the surrounding Walls of the box; to provide a knock-out portion which will break out in a manner to leave a clean-cut hole without ragged-edges.; to provide a knock-out portion of such a construction` that it will receive the blow ofthe ham- 4- mer or 'other implement even though 4said blow is not delivered accurately thereby avoiding any danger of breaking the box by an improperly-delivered blo'w to provide an outlet box havinga conduit-receiving'opening which will facilitate the insertion of.a so-called insulating loom conduit thereinto and will operate .to grip the conduit when inserted and hold it in place, and to otherwise improve outlet or switch boxes, all as willbe more fullyl hereinafter described and then pointed out .1n the claims. y

In order to provide a construction in which the seal or knock-out portion willbe broken out by a relatively light blow, I form said seal or knock-ont portion with a weak or easily-frangible portion near the center thereof and with transverse lines of weakncss which extend from or near the center to'the edge thereof, and I alsopref crably provide said knock-out portion with a weak or easily-frangible portionat the edge thereof. With this arrangement when a blow is struck on the knock-out portion the latter will first crack along-the trans.- verse lines of weakness after which the separate pieces are very -readily broken along their-peripheral line of weakness and acomparativ'ely light blow will accomplish,` the result.

In the preferred embodiment of my in`- vention the knock-out portion is formed so 105 that portions thereof will project above the `circumjacentwalls of the box, thus insuring thatsaid knock-out portion will be struck by the hammer even though the blow is not accurately delivered. This construction has the further advantage that ifthe hammer which is used to knock out the knock-out portion has a head larger in diameter than the opening, the blow of the hammer will be delivered on the knock-out portion in stead of on the walls circumjacent the opening.

In the illustrated embodiment of my invention the conduit-receiving opening is oval in shape andhas a greater length and vention Fi re-1` is a v'ew cfa circular outlet box having my improved knock-out; Fig. 2 is ay sectional view of an outlet box embodying my invention showing a box having knock-out portions onl opposite sides with one of the mock-out portions being broken out, the sections through the knockout portions being taken on a line corresponding to the line Fig. 1; Fig. 3 is a section on the line 1f-Ky, Fig. 1; Fig. 4 is a sectional view similar to Fig. 3 showing a knock-out portion adapted to be broken out by a blow from the outside of the box; Fig. 5is a fragmentary view` showing'themannerin -which the conduit is locked in the aperture; Fig. 6 shows a switch box provlded with my improved knock-out portion; Figs. 7 to 16 show different forms which my invention may assume.

1 indicates a circular cast metal outlet or junction box which is provided with a plurality of sealed openings 2. The seals or knock-out portions 30 of these openings are cast integral with the box and may be arranged so that they can be driven out by means of a blow delivered either from the outside of the box or from the inside therepared to the general or average thickness of of. In Figs. 1 and 2 the seal is' arranged to be broken out by a blow delivered from the inside of the box while in Fig. 4 a construction is shown in which the seal may be broken out by a blow delivered from the outside of the box. My improved seal lis constructed to have a line of weakness at its periphery 3 where it joins the walls of the opening 2 and I may form this line of weakness by making the seal either thin' ner, or more brittle, or both, at its edges.

It is well known when ,molding gray or cast iron that wherever the opposite sides of the mold of sand or other suitable material, come very close to cach other as com- Ithe pattern, the metal at these thin parts becomes'much harder and more brittle, undoubtedly due to the much more rapid cooling, thus forming what is known to the trade as a chill or cold-shot. Sometimes the metal at these points is so hard and brittle that it can hardly be acted upon by a sharp file. ll'hen my improved seal is made thinnest at its edges the above phenomenon takes place and the thin edges are very hard and brittle. The weakness at the edges of my improved seal may thus be partlydue to the fact that the seal is thin at this place, and partly due to the fact that it is brittle at this place. It is not essential to my invention, however, how the line of weakness at the edges of the seal is formed.

lVhile the seal in a cast metal box which is thus made thinnest at its edges to pro- ,vide a line of weakness 3 where it joins the box will break out more or less'readily, yet I prefer to make the seal with a-weak en'ed portion near the center also so that when the blow is struck it will crush down from thecenter as it were, and I also preferto form the seal with transverse lines of :weakness which will preferably, although not necessarily, extend radially from the center to the periphery-of the seal. These ends can be secured by casting the seal with the diametrically-cxtending grooves 4 and 5 `at or near the center of the seal, said grooves being of such a depth as to leave comparatively little metal at the bottom of the groove. These grooves thus constitute -lmes of weakness because of the Athinn'css of the metal at the bottom thereof, and if the metal at the bottom of the grooves f chills 01" cold shots when the casting 1s poured, the brittleness of the metalthus caused constitutes an additional element ot' weakness. Where these grooves are thus formed a blow struck on the center of the seal will first cause it to fracture along the radial lines -l and 5, thus leaving a. plurality of separate sector-shaped pieces (i, each ot' which is integrally connected with the wall of the aperture by the thin edge 3 and can be broken oil' at said edge with very little force, as will be perfectly obvious. lith this arrangement, therefore, a comparatively light blow will not only fracture the seal i' rom the center along the radial lines 4 'and 5, but will also at the same time break the seal out along the weakened edge 3, and leave an aperture with a clear-cut edge.

In striking the seal a blow to break it out. it is not always easy to hit the seal squarelyl and workmen frequentlyhit the eircunijaeent wall of the box instead. If the box is a. cast metal box a blow of this nature may crack or fracture the box. In order to provide a construction whercina blow will inet is large, and also to afford a constructior.l whereby as much of the total area of the seal and knock-out portion as possible can' be maintained at a thickness substantiallv'equivalent to that of the walls of the box, I form the seal with thickened raised portions which extend above the eircumja'- vcent walls of the box and can therefore be i' conveniently hit witha hammer.

' in Figs. 1s ma e whole is ing 2-Wit l the edge of the opening. The grooves 4 and 5 and the convex side of the seal form a plurality of projections or raised portions 7 which .stand above the surrounding walls of the box and can consequently be readily hit with a hammer without danger of striking the walls of the box. 30

`In Fig. 7 an embodiment of my invention is shown in swhieh the transverse or radial lines of weakness are formed by making the seal-.with brittle streaks 21 without form- These brittle or easily-frangible portions can be made by 'water crossing the sand mold or in lany other well known way.

In Fig. 9 a seal 30 is shown having the raised portions 7l situated near the edge thereof and with a concavity 22 in the center. These raised portions will preferably be separated by radial lines of weakness.

In Fig. 10 I have shown an embodiment -of my invention having all the features thereof illustrated in Figs. 1-3 with the exception of the raised portions which stand above the circumjaeent walls of the box. In this embodiment the seal 3OVis. plane on its upper face and convex on the lower face, but neither face projectsabove or beyond the circumjacent walls of the box.

The seal, however, has the weakened edge 3 andthe ltransverse lines of weakness 4 and v5, so that the seal lcan -be readily broken out by a light blow of the hammer.

In Fig. 11 I have shown a seal 30, both sides of which are plane or flat, but which is so situated in the opening 2 that one side thereof projects above the circumjacent walls of the aperture. This seal is also provided with the weakened edges 3 where it joins tothe walls of the box, the weakcned edges being' provided bymaking them thinner than the body of the seal.

In Fig. 12 a seal 30d isshown similar to asi"l thatshown in Fig. 11 with the exception that the projecting face of the seal is provided with transverse or radial lines of weakness 4 and 5 formed by making transverse or radial grooves. l

In Fig. 13 I have shown a form of seal in which the projecting hammer-.receiving portions 'i'e are at the edges of the seal. This seal is somewhat similar 'in shape to that shown in Fig. 9 except that the raised portions 7 are at the extreme edge of the seal. This seal hasthe central concavity 22 to form a weakened portion at the center of the.

seal and the raised portions 7 rated by thin portions to form of weakness.

In Fig. 14 I have shown another embodiment of my invention wherein the seal 30f is provided with a concavity 22t in the center and with the thickened portions 7 adjacent the edges of the seal. This-seal and also that shown-in' Fig. 13 is joined to the walls of the .box by thin portions .3 which forlm annular lines of weakness around the sea In Fig. 15 I have shown a .double convex can be separadial lmes seal 30g, both sides of which are convex and which is joined to the walls of thebox by the annular line of weakness 3.

In Fig. 16 I have shown a seal 30h having plane pr flat sides one of whieh,is situa-ted above the circumjacent walls of the box thereby to form a hammer-receiving surface. This seal can be provided with central and transverse lines of weakness either by` making the seal with brittle portions or streaks or by making the seal with grooves. The seal is joined to the walls of the' box by an annular line of weakness 3 as above described.

There are various other shapes which a seal embodying my invention mi ht assume, but having suggested the above s apes I do not regard it as necessary to illustrate other possible varieties.

'In all of the above embodiments of my invention the seal is connected to the walls of the box by a weakened portion which will be readily broken when the seal is struck a light blow thereby to leave a clean-cut opening. In the preferred embodiments of my invention the seal is also provided with transverse or radial lines of weakness which may be either securedby making the seal with'brittle or easily-frangible lines or byA making the seal with transverse grooves. I

vIn Fig. 6 I have shown a switch box 60 Ahaving my improved seal therein, said seal the conduit-receivmg o enings of non-circular form and of suchd imensions that they will have lesser width and greater length than the normal diameter 'of the insulating turned on its axis the bulgcd portions of the.

loom are carried around against the flattened sides of the conduit so as to cause an increaled gripping engagement at this` point. The conduit is thus iirmlyanhored in the opening. Under some circumstances I may place two of the conduit-receiving openings in such position relative to each other that they will intersect eachother, as shown at the top in Fig. 1, thereby providing a double-conduit-receiving opening.

It will be noted from an inspection of Figs. 2 and 3 that the conduit-receiving openings 2 have tapered walls. The inner terminus of the opening is made of a greaterlength and lesser width than the normal diameter of the loom 61, as clearly seen in Fig. 5', and the tapering walls of the opening are of very reat advantage in facili'- tating the insertion of the loom into the oblong opening. It will be readily' perceived that if the opening was of the size shown in Fig. 5 throughout its entire length, itA

would be somewhat difficult toV insert the loomtherethrongh, for the loom would have to be compressed by hand to fit the openingbefore it could be inserted ,thereinto. Where the opening has the tapering walls or funnel shape seen in Figs. 2 and 3, the operation of inserting the loom in the opening requires no manipulation of the loom other than a forcing oi it longitudinally through the funnel-shaped opening, for the size of the opening at the lou` er cud is sufficient to receive the loom without distorting it, and as the loom is Ainserted it becomes forced into its elliptical shape by engagement with the tapering walls.

The double conduit-receiving opening shown at the top of Fig. 1 has the advantage that when two insulating loom conduits are inserted thercinto they will wedge against each other and thus serve t0 bind each other 1n the opening. -My improvements are applicable not only to outlet boxes, but to sofcalled junction boxes and switch boxes and the like, and by the term outlet box as used in the appended claims I intend to include any box of this nature whether it is a junction box, switch box, or so-called outlet box.

Having fully described my invention,

2. A east metal outlet box havingcast integral therewith a lmock-out portion which is easily frangible along a line extending transversely thereof and which' has a. portion extending above the circumjacent walls of the box. 'l l y 3. A cast metal outlet box having east integral therewith a knock-out portion Lich is easily frangible along two intersecting transversely-extending lines and which has a portion extending -beyond the circumjacent walls of the box.` g

4.v A cast Vmetal outlet box having cast integral therewith a knock-out portion which is easily f rangible along lines extending both transversely and circumferentially thereof and which has a portion extending above the circumjacent walls of the box.

."In' an electric switch box, the combination.- with the flexible tubular insulating loom, of a box having wire openings therein of le'sser width'and greater length than the i ing a conduit-receiving passage extending through the wall thereof, which passage iS provided with inclined walls and has' a greater diameter at the outer end than at the inner end thereof, said inner end of the passage being of greater length and lesser width than the normal outside diameter of the loom. f

8. The combination with flexible tubular insulating loom, of an-outlet box having two intersecting conduit-receiving openings, each having a' greater diameter and a lesser length than the4 normal outside diameter of the loom.

In testimony whereof, I have signed ymy name to this specification, in the presence of two subscribing witnesses.

MINER ROBINSON.

. lVitnesses t LoUIs C. SMITH, BERTHA F. HEUSER.

i lt is hereby certified that in Letters Patent No. 1,121,291, granted DecemIber 15, 1914, upon the application of Miner Robinson, of Newton, Messachusetts,` for an improvement in Outletslor Switch Boxes, un error appears in the printed-specification requiring correction as follows: Page-4; line 96, for` the compound word conductfreoeiving read conduit-receiving; andthat the said Letters Patent should be read with this correction therein that the same inay conform to the record of the case in the PutenhOilice. I

Signed and sealed this 26th day of Jennery, A. D., 1915,

[SEAL] I i R. F. WHITEHEAD,

Acting Commissioner of Patmts. 

